1. Field of the Invention
The present invention relates to a fabricating apparatus of semiconductor device, and more particularly to a vacuum plate of a low pressure chemical vapor deposition (LPCVD) apparatus that makes an exhaust flow uniform.
2. Description of the Related Art
Generally, LPCVD is a kind of chemical vapor deposition (CVD) in which a thin film is formed on a substrate by using a chemical reaction of chemical gases, and has a characteristic that a reaction pressure of the chemical gases is lower than an atmospheric pressure. In the LPCVD, that is, reactants of gas phase are chemically reacted under a pressure lower than the atmospheric pressure, thereby a product is deposited onto the substrate to form a thin film.
FIG. 1 is a schematic cross-sectional view of a conventional LPCVD apparatus.
In FIG. 1, the conventional LPCVD apparatus includes a single substrate type chamber 10 of a vertical furnace, a gas supplying unit 50 that stores and supplies the chamber 10 with reactants, and an environmental control unit 60 that controls an interior pressure of the chamber 10 low. A substrate 5 is loaded in the chamber 10 of sealed reaction vessel.
The gas supplying unit 50 includes a storage tank “T” stored with the reactants, and a plurality of tube type injectors 54a and 54b for injecting and diffusing the reactants of the storage tank “T” into the chamber 10. The plurality of tube type injectors 54a and 54b are vertically equipped to penetrate a bottom surface 12 of the chamber 10.
Preferably, the single substrate type chamber 10 includes a susceptor 20 having a heater 22 to heat the substrate 5 up for increasing a deposition rate. The substrate 5 is loaded on the susceptor 20 and a product of the chemical reaction of the injected reactants is deposited onto the substrate 5.
The environmental control unit 60 includes an exhausting tube 64 equipped to penetrate the bottom surface 12 of the chamber 10, and a vacuum pump “P” connected to the exhaust tube 64.
An inner pressure of the chamber 10 is controlled lower than the atmospheric pressure by the environmental control unit 60, and the reactants are supplied to the chamber 10 by the gas supplying unit 50. Accordingly, a thin film is formed on the substrate 5 through adsorption, decomposition, reaction and segregation between the reactants. Since the inner pressure of the chamber 10 is lower than the atmospheric pressure, a mean free path of the reactants is elongated. Accordingly, a concentration of the reactants becomes uniform over the substrate and it is easy to segregate residues on the substrate after the reaction.
In the LPCVD apparatus, the deposition rate “D” of the thin film may be expressed by the Arrenius equation as follows.D=kPnexp(−Ea/kT),
where k is a constant, P is a pressure of the chamber (reaction vessel), Ea is an activation energy of reaction gases and T is a temperature of the substrate. According to the Arrenius equation, a uniform pressure and a uniform temperature are essential for fabricating a uniform thin film in the LPCVD apparatus.
Especially, in the single substrate type chamber 10 (of FIG. 1) compared with the batch type chamber, since the thin film is deposited with a very high deposition rate, the injection pressure of reaction gases and the exhaust pressure are also very high. Accordingly, reaction gases may stay in the single substrate type chamber for short periods of time and it is very hard to adjust the pressure of the single substrate type chamber uniform.
For the purpose of keeping a uniform pressure over the substrate, the injecting pressure of reaction gases and the exhaust pressure of residual gases should be kept uniform. Especially, since the higher exhaust pressure is required to keep a low pressure during the reaction process in the chamber for the LPCVD apparatus, the uniform exhaust pressure is an essential element for the uniform pressure over the substrate. As the exhaust pressure becomes non-uniform, a gas flow over the substrate also becomes non-uniform. Accordingly, the thin film deposited on the substrate does not have uniform thickness and a bit of powder resulting from vapor phase reaction of three-dimensional nucleation is generated in the chamber.
To prevent the non-uniformity of the exhaust pressure, an apparatus in which the exhaust tube 64 is equipped at the center of the bottom surface 12 of the chamber 10 may be considered. Generally, however, the susceptor 20 and a plurality of devices for driving the susceptor 20 are equipped at the center of the bottom surface 12 of the chamber 10. Therefore, the exhaust tube 64 cannot be actually equipped at the center of the bottom surface 12 of the chamber 10. To solve these problems, a vacuum plate 30 for the uniform gas flow over the substrate is equipped at the bottom surface 12 of the chamber 10.
FIG. 2 is a schematic disintegrated view showing a structure of a conventional vacuum plate for an LPCVD apparatus.
In FIG. 2, the conventional vacuum plate 30 includes an upper vacuum panel 30a and a lower vacuum panel 30b. The upper vacuum panel 30a has an upper susceptor hole 36a at its center and a plurality of upper injector holes 32a, 32b, 32c, 32d and 32e spaced apart from the upper susceptor hole 36a. The lower vacuum panel 30b also has a lower susceptor hole 36b at its center and a plurality of lower injector holes 33a, 33b, 33c, 33d and 33e spaced apart from the lower susceptor hole 36b. The upper and lower vacuum panels 30a and 30b are combined and equipped on a bottom surface 12 of a chamber. A susceptor and a plurality of devices for driving the susceptor (not shown) are equipped through the upper and lower susceptor holes 36a and 36b. Further, a plurality of injectors 54a, 54b, 54c, 54d and 54e are equipped through the plurality of upper and lower injector holes 32a, 33a, 32b, 33b, 32c, 33c, 32d, 33d, 32e and 33e, respectively.
The upper vacuum panel 30a includes a plurality of exhaust holes 34 and the lower vacuum panel 30b includes a pumping hole 40 to which one end of an exhaust tube 64 (of FIG. 1) is connected. Air flowing into the vacuum plate 30 through the plurality of exhaust holes 34 is exhausted through the pumping hole 40. An exhausting means such as a pump “P” which belongs to the environmental control unit 60 (of FIG. 1) is connected to the other end of the exhaust tube 64 (of FIG. 1).
If the interior of the chamber does not obtain ultra high vacuum or plenty of gases are not injected when a thin film is deposited by using the conventional vacuum plate 30 of the said structure, a phenomenon of non-uniform exhaust pressure happens. Since the interior of the chamber is exhausted through a pumping hole 40 that is asymmetrically located in the lower vacuum panel 30b, after the upper and lower vacuum panels 30a and 30b are combined, the exhaust flow is slanted. An exhaust pressure (the suction) at a portion “A” of the plurality of exhaust holes 34 formed on the upper vacuum panel 30a is higher than that at the other portions. Accordingly, unless the chamber is exhausted through the exhaust holes of the other portions except the portion “A” due to supplying plenty of gases or is kept an ultra high vacuum during the deposition of the thin film, a phenomenon of non-uniform exhaust pressure that an exhaust pressure at a portion “A” is higher than that at the other portions happens.